Symmetrical linear Co36+ chains cocooned by two polypyridylamide ligands: How do they compare to open chains?
摘要:
Two extended metal atom chain (EMAC) compounds having a symmetrical Co-3(6+) metal chain encapsulated by two N,N'-bis[(6'-pyrid-2 ''-yl)aminopyrid-2'yl]-bismethyl-2,6-diaminopyridinate (mpeptea) ligands have been prepared in good yield, and they have been structurally characterized by X-ray crystallography, magnetic and electrochemical measurements and spectroscopic techniques. For the EMAC [Co-3(mpeptea)(2)]Cl-2 two solvates have been crystallized. Anion exchange has also allowed isolation of [Co-3(mpeptea)(2)](BPh4)(2). In these three species the Co-3(6+) units are cocooned within two polypyridine ligands having nine nitrogen atoms although only seven of these coordinate to the metal centers. The cations [Co-3(mpeptea)(2)](2+) are similar and have Co center dot center dot center dot Co separations of ca. 2.3 angstrom at 213 K. These distances are consistent with partial bond formation between Co atoms. Electrochemical measurements show a unique one-electron oxidation process that differs from that in open chain species which show two reversible oxidation processes. At 300 K, the chi T value is 7.32 emu K mol (1) but this value drops to 1.47 emu K mol (1) as the temperature is lowered to 2 K. The X-band EPR spectra for Co-3(mpeptea)(2)(2+) show g values of 2.3 at room temperature. The magnetic behavior is quite different from that in compounds with open Co-3(6+) units. A discussion is provided. (C) 2010 Elsevier B. V. All rights reserved.
A trimetal chain cocooned by two heptadentate polypyridylamide ligands
作者:F. Albert Cotton、Hui Chao、Carlos A. Murillo、Qingsheng Wang
DOI:10.1039/b612076h
日期:——
Compounds of nickel in which a chain of three metal atoms is closely embraced by two interlocking heptadentate dianions derived from a chain of five pyridyl groups linked at the 2, or 2 and 6, positions by four amide nitrogen atoms are reported. This new type of extended metal atom chain (EMAC) compound differs from earlier ones in that ligand exchange at the axial positions cannot occur, because the axial ligands are part of the entire ligand. Four such compounds, all crystallographically characterized, are reported. This work is a proof-of-concept project that will be extended to other metals with these and other homologous ligands.
Symmetrical linear Co36+ chains cocooned by two polypyridylamide ligands: How do they compare to open chains?
作者:F. Albert Cotton、Carlos A. Murillo、Qingsheng Wang
DOI:10.1016/j.ica.2010.04.045
日期:2010.12
Two extended metal atom chain (EMAC) compounds having a symmetrical Co-3(6+) metal chain encapsulated by two N,N'-bis[(6'-pyrid-2 ''-yl)aminopyrid-2'yl]-bismethyl-2,6-diaminopyridinate (mpeptea) ligands have been prepared in good yield, and they have been structurally characterized by X-ray crystallography, magnetic and electrochemical measurements and spectroscopic techniques. For the EMAC [Co-3(mpeptea)(2)]Cl-2 two solvates have been crystallized. Anion exchange has also allowed isolation of [Co-3(mpeptea)(2)](BPh4)(2). In these three species the Co-3(6+) units are cocooned within two polypyridine ligands having nine nitrogen atoms although only seven of these coordinate to the metal centers. The cations [Co-3(mpeptea)(2)](2+) are similar and have Co center dot center dot center dot Co separations of ca. 2.3 angstrom at 213 K. These distances are consistent with partial bond formation between Co atoms. Electrochemical measurements show a unique one-electron oxidation process that differs from that in open chain species which show two reversible oxidation processes. At 300 K, the chi T value is 7.32 emu K mol (1) but this value drops to 1.47 emu K mol (1) as the temperature is lowered to 2 K. The X-band EPR spectra for Co-3(mpeptea)(2)(2+) show g values of 2.3 at room temperature. The magnetic behavior is quite different from that in compounds with open Co-3(6+) units. A discussion is provided. (C) 2010 Elsevier B. V. All rights reserved.